1. Technical Field
This disclosure relates generally to microwave-frequency (microwave) alternating current (AC) conductivity in dielectric or semiconducting materials. Specifically, the disclosure pertains to configuring and tuning microwave AC conductivity in ferroelectric materials for electronic and microwave device elements.
2. Related Art
In ferroelectric materials, domains of uniform polarizations may be separated by domain walls. Domain walls may have a lateral width of only a few nm. The concept of domain wall electronics and utilization of domain walls and other topological defects within ferroelectric materials has been pursued in view of electronic device applications. Despite the electrically insulating nature of ferroelectric materials, several types of ferroelectric domain walls have exhibited direct current (DC) conduction. However, understanding of domain wall conduction mechanisms and progress towards practical utilization of domain wall circuits have so far been impeded by the low conduction observed in domain wall materials and the large ferroelectric-electrode contact resistance.
Efforts to measure domain wall current flow have relied on relatively large DC voltage biases resulting in highly rectifying current-voltage characteristics with detectable current at only one bias polarity. The issue of contact resistance has been particularly important. A contact interface Schottky barrier conceals the intrinsic mechanisms of charge transport along in-depth regions of domain walls. Although the contact resistance can be overcome with a sufficiently large applied bias, such an electric field applied in the contact junctions generally becomes comparable to or exceeds coercive fields for domain wall motion and even polarization reversal (switching). Therefore, resistive readout at DC is generally destructive as it readily causes the loss of domain wall stability and is capable of displacing and erasing the domain walls. These effects have severely limited the prospects of domain wall circuits, particularly in materials with desired low coercive fields.